1. Field of use
While the invention is subject to a wide range of applications, it is especially suited for use in a system for mixing oxygen with industrial waste and will be particularly described in that connection.
2. Description of the Prior Art
Mixing apparatuses biochemically treat BOD-containing waste water, such as municipal sewage, by oxygenation. This has customarily been accomplished by providing a sparge ring in a tank beneath an impeller. The impeller circulates the sewage and the sparge ring introduces the oxygen into the tank to be mixed. For example, see U.S. Pat. No. 3,227,701 to Pennington and U.S. Pat. No. 3,547,813, to Robinson, et al.
In one known biochemical oxidation process, sewage is mixed with oxygen-containing gas, such as air, and activated sludge. The latter consists essentially of aerobic organisms which have the ability in the presence of sufficient dissolved oxygen to absorb and assimilate the biochemically oxidizable organic material of the municipal sewage, thereby converting the organic material to forms which can be separated readily from the purified water. Under normal conditions the bacteria multiply rapidly in the aeration tanks during this treatment step. When the requisite period of BOD conversion is complete, the mixed liquor is settled, the purified affluent decanted to receiving waters, and sludge is withdrawn from the bottom of a clarifier.
As pointed out above, it is known to use a sparge ring to supply oxygen-containing gas to the waste water. The sparge ring would be placed beneath a circulating impeller with the gas traveling to the suction side of the impeller. The impeller generally rotates at a fixed speed. When the sparge ring is supplying gas to the tank, the impeller is drawing a gassed power. When the sparge ring is not supplying gas to the tank, the impeller is drawing an ungassed power. The ratio of ungassed power to gassed power is known as the K Factor. Generally, the K Factor is quite low since the system draws more power when ungassed. This is because it requires more torque to rotate the impeller through liquid than through liquid and gas. Therefore, if a motor for the impeller is designed to operate at a given gassed power, and someone accidentally turns off the gas, the power drawn increases and the motor may be damaged.
It is an object of the present invention to provide an apparatus for mixing a liquid with a gas.
It is a further object of the present invention to provide a mixing apparatus than can operate in a gassed or ungassed condition without concern for overloading the motor that drives the impeller.
It is a further object of the present invention to provide an apparatus for mixing a liquid with a gas at a higher power level to increase the mass transfer rate.
It is a further object of the present invention to provide an apparatus for mixing a gas with a liquid being circulated by a radial flow turbine.